//类
class Customer

//属性
class Contact(val id: Int, var email: String)

class Contact1(val id: Int, var email: String) {
    val category: String = ""
    fun printId() {
        println(id)
    }
}

//数据类
data class User(val name: String, val id: Int)

fun main() {
    //创建实例
    val contact = Contact1(1, "sa")
    //访问属性
    println(contact.id)
    contact.printId()
    println(contact)
    val user = User("a", 1)
    println(user)
}